Micro-electromechanical systems (“MEMS”) and nano-devices typically include three-dimensional (“3D”) structures made from photoimaged materials. In some applications, it is necessary for the 3D structures to have varying degrees of physical and/or mechanical properties across a thickness of the photoimaged material. Examples of MEMS and nano-devices, include, but are not limited to fluid ejection heads, micro-filters, micro-separators, micro-sieves and other micro and nano scale fluid handling structures. Such structures may handle a wide variety of fluids. For example, fluid ejection heads are 3D nano-devices that are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used fluid ejection head is in an ink jet printer. However, fluid ejection heads may also be used in vaporization devices for vapor therapy, E-cigarettes and the like. New techniques are constantly being developed to provide low cost, highly reliable fluid ejection heads for such devices.
The fluid ejection head is a seemingly simple device that has a relatively complicated structure containing electrical circuits, ink passageways and a variety of tiny parts assembled with precision to provide a powerful, yet versatile fluid ejection head. The components of the ejection head must cooperate with each other and be useful for a variety of fluids and fluid formulations. Accordingly, it is important to match the ejection head components to the fluid being ejected. Slight variations in production quality can have a tremendous influence on the product yield and resulting ejection head performance.
The primary components of a fluid ejection head are a semiconductor substrate, a flow feature layer, a nozzle plate layer, and a flexible circuit attached to the substrate. The semiconductor substrate is preferably made of silicon and contains various passivation layers, conductive metal layers, resistive layers, insulative layers and protective layers deposited on a device surface thereof. Fluid ejection actuators formed on a device surface of the substrate may be thermal actuators or piezoelectric actuators. For thermal actuators, individual heater resistors are defined in the resistive layers and each heater resistor corresponds to a nozzle hole in the nozzle plate for heating and ejecting fluid from the ejection head toward a desired substrate or target.
Current methods used to make the fluid flow layer and nozzle plate layer involve the use the combination of spin on photoresist or dry film photoresist with multiple image, develop, and bake steps for each layer. For example, in a conventional process, a first adhesion promotion layer is applied to a semiconductor substrate, a fluid flow layer of photoimageable material is spin coated onto the adhesion layer. The fluid flow layer is a negative photo resist layer that is imaged, cured, and developed. A second adhesion promotion layer is applied to the fluid flow layer before applying a nozzle layer. Next the photoimageable layer nozzle layer is laminated as a dry film to the fluid flow layer by means of the secondary adhesion promotion layer. The nozzle layer is imaged, cured and developed. The semiconductor substrate is then deep reactive ion etched (DRIE) to form vias through the substrate. Since the fluid flow layer and nozzle layer are already attached to the substrate, the process latitude for the DRIE process is limited.
In an alternative process, the semiconductor substrate is first etched to form vias using the DRIE process before or after an adhesion promotion layer is applied to the substrate. Then the fluid flow layer and nozzle layer are applied to the substrate as dry films that are each imaged and developed. Each dry film requires a separate adhesion promotion layer. There is a risk of adhesion loss between layers with the application of each additional adhesion promotion layer.
In a variation of the alternative process, the DRIE process is conducted after the fluid flow layer is applied to the substrate and is imaged and developed. Subsequent to the DRIE process, the nozzle layer is laminated to the fluid flow layer and is imaged and developed.
Regardless of the process used, the use of multiple layers requiring multiple adhesion promotors increases the process time for making the fluid ejection heads and increases the risk of loss due to adhesion layer failure. Also, the MEMS or nano-scale devices having a 3D structure may require a layer that is hydrophilic and a layer that is hydrophobic in order to efficiently process a fluid through the device. The mechanical properties of the layers may also be different depending on the uses of the MEMs or nano-device. Accordingly, what is needed is a 3D structure and method for making the structure that enables varying physical and/or mechanical properties through a thickness of a composite photoresist layer that can be applied to a substrate with a single adhesion layer.
The disclosure provides a three-dimensional (“3D”) structure for handling fluids, a fluid handling device containing the 3D structure, and a method of making the 3D structure. In one embodiment, the method includes providing a composite photoresist material that includes: (a) a first photoresist layer derived from a photoresist resin having a first chemical property selected from the group consisting of epoxide equivalent weight, aromatic content, and crosslink density and (b) at least a second photoresist layer derived from a photoresist resin having a second chemical property selected from the group consisting of epoxide equivalent weight, aromatic content, and crosslink density different from the first chemical property. The composite photoresist material is devoid of an adhesion promotion layer between layers of the composite photoresist material and the composite photoresist material has varying mechanical and/or physical properties through a thickness of the 3D structure.
In another embodiment, there is provided a method for making a three-dimensional (“3D”) structure from a composite photoresist film. The method includes the steps of: (A) applying a first layer of photoresist material to a carrier film, the first layer being derived from a photoresist resin having a first chemical property selected from the group consisting of epoxide equivalent weight, aromatic content, and crosslink density; (B) drying the first layer to provide a dried first layer; (C) applying a second layer of photoresist material to the dried first layer, the second layer being derived from a photoresist resin having a second chemical property selected from the group consisting of epoxide equivalent weight, aromatic content, and crosslink density different from the first chemical property; (D) drying the second layer to provide a composite photoresist material devoid of intermediate adhesion layer(s); (E) applying an adhesion layer to a substrate surface; (F) laminating the composite photoresist material to the adhesion layer; (G) exposing the composite photoresist material to a first radiation exposure wavelength selected from e-line, g-line, h-line, i-line, mid ultraviolet (UV), and deep UV radiation; and (H) simultaneously developing the composite photoresist material to provide the 3D structure having varying mechanical and/or physical properties through a thickness of the 3D structure.
Another embodiment of the disclosure provides a fluid ejection device having a fluid ejection head that includes a semiconductor substrate containing a plurality fluid ejection actuators on a device surface thereof and one or more fluid supply vias etched therethrough. An adhesion promotion layer is applied to the device surface of the semiconductor substrate. A composite photoresist material is applied to the adhesion promotion layer wherein the composite photoresist material contains (a) a first photoresist layer derived from a photoresist resin having a first chemical property selected from the group consisting of epoxide equivalent weight, aromatic content, and crosslink density and (b) at least a second photoresist layer derived from a second photoresist resin having a second chemical property selected from the group consisting of epoxide equivalent weight, aromatic content, and crosslink density different from the first chemical property. The composite photoresist material is devoid of an adhesion promotion layer between layers of the composite photoresist material. A controller for activating the fluid ejection head is also provided.
In some embodiments, the composite photoresist material includes at least a third layer of photoresist material, wherein the third layer of photoresist material is derived from a third photoresist resin having a third chemical property selected from the group consisting of epoxide equivalent weight, aromatic content, and crosslink density that is different from the first and second chemical properties.
In some embodiments, the composite photoresist material has a thickness ranging from about 6 to about 150 μm.
In some embodiments, the composite photoresist material is imaged with a radiation exposure wavelength selected from e-line, g-line, h-line, i-line, mid ultraviolet (UV), or deep UV radiation.
In some embodiments, each photoresist layer of the composite photoresist material is imaged with a different radiation exposure wavelength selected from e-line, g-line, h-line, i-line, mid ultraviolet (UV), or deep UV radiation.
In some embodiments, one or more layers of the composite photoresist material includes a hydrophobicity agent.
A benefit of manipulating the mechanical and/or physical properties of each layer of the composite photoresist material is the ability to reduce stresses in MEMS or nano-devices. Accordingly, embodiments of the disclosure simplify and enable multiple layers of MEMS and nano structures to have varying mechanical and/or physical properties for use in a wide variety of applications.
Another advantage of the embodiments described herein is that the process steps for making 3D MEMS and nano-devices are greatly simplified as described in more detail below and provides devices in higher yields due to a decrease in lamination adhesion failures.